The present invention relates to opto-electronic substrates that may be used to connection digital and/or analog electronic systems, and methods for making such systems. More specifically, the present invention relates to opto-electronic substrates that have both electrical and optical interconnections, and methods for making such substrates. The present invention may be applied to multichip modules (MCMS) and the like.
With the increase in clock rates and I/O counts of processing systems implemented on interconnection substrates, the problems of interconnection bottlenecks, noise, signal attenuation, heat generation, and maintaining synchronizable connection lengths in the electrical connections of such systems are appearing. An optical interconnect has the advantage of low RC delay, low signal attenuation, predictable delay, low power, low noise and high tolerance to opens and shorts. However, there is a large barrier which prevent optical interconnections from being used in high-speed digital/analog systems. Thus far, bulky driver chips and amplifier chips have been required to provide the conversions between the optical signals in the optical interconnects and the electrical signals which are generated and used by the electronic chips. Each electrical signal that is to be convey optically over a long distance requires a light emitting device, a driver chip to generate the electrical power for switching the light-emitting device at one end of the optical connection. At the receiving end of the optical connection, a photo-detector device and an amplifier is required to convert the optical signal to electrical form. The amplifier is needed because the light power becomes small at the photo-detector device due to considerable loss in conventional optical paths. The driver and amplifier components require space on the circuit substrate, and therefore represent barriers to using large numbers of optical connections in a substrate, like a multichip module. In fact, the area needs of these components, as well as the area needs for the emitter devices and photo-detector devices, would increase the size of the module substrates to be larger than module substrates with pure electrical connections. These excess components and their assembling increase manufacturing costs. Furthermore, the conventional optical connections have longer delay due to EO and OE conversions, which would not provide significant speed benefits over pure electrical modules.
The present application is directed to providing optical connection configurations and methods for manufacturing the optical connections such that the above problems may be overcome.
One aspect of the present application eliminates the need for the bulky drivers and amplifiers, which significantly reduces area requirements. In the place of a light-emitting source, the combination of an external light-source and an optical switch device (e.g., modulator) is used. The optical switch device is responsive to an output of an IC chip, and does not required a driver chip for operation. In contrast to light emitting source cases, the power of optical signals in implementations using light modulators can be greatly increased by increasing the size and power of the external light source. The external light source can be easily increased in this manner since it does not need to be modulated. For example, it can be implemented as a simple continuous wave (CW) or pulse trains source of optical power. In addition, losses in the optical connection are reduced. Therefore, and power at the photo-detectors is increased, which enables the amplifiers to be eliminated. The losses are reduced by integrally forming polymeric waveguides with the optical switches and the photo-detectors, which increases optical coupling efficiency. Additionally, the construction methods of the present invention enable short optical connections to be made. Optical power to the photo-detector device is increased by using the external optical power. In addition, optical waveguide integration methods of the present invention enable highly efficient optical connections to be made to VCSEL and laser-diode (LD) emitter devices, which enables these devices to be used as sources of optical power in addition to external sources.
Another aspect of the present application realizes device and/or material integration into an xe2x80x9copto-electronic (OE) layerxe2x80x9d, which increases room for chip-mounting, and reduces the total system cost by eliminating the difficulty of optical alignment between OE devices and optical waveguides. OE devices can be embedded into waveguide layers by using wafer processing techniques according to the present invention. Methods according to the present invention enable opto-electronic devices (e.g., modulators, VCSELs, photo-detectors, optical switches, laser-diode (LD), driver chips, amplifier chips, etc.) to be integrated with optical waveguides in ultra thin polymer layers on the order of 1 xcexcm to 250 xcexcm.
Another aspect of the present application provides OE substrates by stacking the above-described OE layers on top of one another and by joining them together, such as by lamination or by a build-up fabrication process. The OE layers can then be overlaid upon the surface of a conventional electrical substrate without requiring extra room for the photo-detectors, optical-switches, light-emitting components, driver chips, amplifier chips, etc. In fact, multiple OE layers can be stacked upon one another to provide all the required photo-detectors optical-switches, light-emitting devices, driver chips, amplifier chips, etc. The present application provides several construction methods for forming these OE layers, and also provides several substrate configurations.
Another aspect of the present application is a method to stack two or more OE films, permitting an increase in the functionality of the stacked structure compared to a single OE film. Each OE film may comprise a single-layer structure or be build-up-of multiple-layer structures, including electrical layers by a Z-connection method. The OE layers and electrical layers on each OE film may be optimized separately. Preferred embodiments of stacked OE films include flexible interconnections, OE Interposers, film OE-MCM, both-side packaging, back-side connection, and a Film Optical Link Module (FOLM). Additionally, stacked films permit the use of a greater variety of fabrication processes compared to a single film. In particular, a stacked film enables both-side processing by permitting processed layers to be inverted upside-down.
One embodiment of the invention provides an optoreflective structure for reflecting an optical signal following a path defined by an optical waveguide comprising a first cladding layer having a first planar cladding surface; a waveguide disposed on the first cladding layer; and a second cladding layer disposed on the waveguide and having a second planar cladding surface. The first cladding layer, the second cladding layer and the waveguide terminate in a beveled planar surface, and an optoreflector is disposed on the beveled planar surface for changing a direction of an optical signal passing through the waveguide.
Another embodiment of the invention provides an optoreflective structure for reflecting an optical signal following a path defined by an optical waveguide comprising a first cladding layer having a first planar cladding surface; a waveguide disposed on the first cladding layer; and a second cladding layer disposed on the waveguide and having a second planar cladding surface. This first cladding layer, the second cladding layer and the waveguide terminate in a generally dove-tailed structure having a beveled planar surface, and an optoreflector is disposed on the beveled planar surface for changing a direction of an optical signal passing through the waveguide.
Embodiments of the present invention also provide a number of methods for producing an optoreflective structure. One method comprises: providing a substrate supporting a first cladding layer having a first planar cladding surface; disposing a waveguide material on the first cladding layer; forming on the waveguide material a second cladding layer having a second planar cladding surface; forming a beveled planar surface in the first cladding layer, in the waveguide material, and in the second cladding layer; and depositing an optical signal-changing surface on the beveled planar surface. Another method comprises providing a substrate supporting a first cladding layer having a first planar cladding surface; disposing a waveguide material on the first cladding layer; forming on the waveguide material a second cladding layer having a second planar cladding surface; forming in the first cladding layer, in the waveguide material, and in the second cladding layer a generally dove-tailed structure having a beveled planar surface; and depositing an optical signal changing surface on the beveled planar surface. A further method for producing an optoreflective structure comprises forming a first waveguide layer; forming a first waveguide column in communication with the first waveguide layer; forming a second waveguide column in communication with the first waveguide layer; and forming a second waveguide layer in communication with the first waveguide column and with the second waveguide column.
Another aspect of the present application is to provide three-dimensional opto-electrical modules, and methods for making, which provide for Z-direction waveguides formed perpendicular to the plane of a stack of OE, waveguide, and chip layers, and which interconnections between the Z-direction waveguides and waveguides in the stack of layers.
These features provide the advantageous effect of enabling large-scale optical interconnections to be added to electrical substrates without increasing area requires of the substrate. These features also enable the optical coupling efficiencies of optical interconnections to be increased. These features are also applicable to optical-parallel-link modules.
In the present application, examples of multichip modules are principally shown. However, the same features and aspects of the present invention are applicable to electrical backplanes, printed-circuit boards (PCBs), chip size packages (CSPs), and other substrates.